Researchers at Massachusetts General Hospital have presented Phase II clinical trial results showing that BCG (Bacillus Calmette‑Guérin), one of the oldest vaccines – developed in the 1920s against tuberculosis – can significantly reduce insulin use in patients with autoimmune forms of diabetes.
The data, released at the American Diabetes Association congress, support the hypothesis that live attenuated vaccines have therapeutic potential beyond their original disease targets.
The study enrolled 95 people with latent autoimmune diabetes in adults (LADA) – a condition often mistaken for type 2 diabetes – plus a separate cohort with classic type 1 diabetes.
Participants in the active arm received six BCG injections over five years, while the control group received a placebo.
The key finding was not a direct drop in glucose levels but a slowing of the destruction of pancreatic beta cells, which produce insulin and are attacked by the immune system in autoimmune disease.
In the placebo group, average insulin consumption rose by 22% over the study period. In contrast, patients who received BCG saw their insulin use fall by an average of 3%.
The authors say this points to an immunomodulatory effect of the vaccine, suppressing the body’s attack on its own cells.
“This opens new possibilities for diabetic patients to achieve blood sugar control without constantly increasing insulin doses or introducing expensive new devices,” said study leader Denise Faustman, director of the immunobiology laboratory at Massachusetts General Hospital.
Industry experts, including immunologist Mihai Netea of Radboud University, called the results “exciting” but noted that BCG’s mechanism of action needs further study and that the effect, while statistically significant, remains modest in absolute terms.
The findings also reinforce the trend of studying live‑pathogen vaccines as a platform for treating autoimmune diseases. That could attract investment into Phase III clinical trials, which would be needed to potentially expand BCG’s approved indications.
BCG, used since the 1920s against tuberculosis, is based on a weakened strain of Mycobacterium bovis. Over time, it has also been shown to protect against leprosy and other mycobacterial infections, is used to treat bladder cancer, and is being studied for many other diseases. The U.S. FDA has also approved it for bladder cancer therapy.
The vaccine is also under investigation for Alzheimer’s disease.
Diabetes has emerged as another promising avenue. Previous experiments showed that BCG can suppress the development of type 1 diabetes in mice and lower blood sugar in people with the disease.
The drug was also tested to reduce inflammation in COVID‑19, but as a preventive measure against the disease, the vaccine did not live up to expectations.